Persons with xeroderma pigmentosum (XP), an inherited disease, tend to form tumors on body surfaces, including the conjunctiva of the eye, exposed to sunlight or to other sources of ultraviolet light (UV). A study done in collaboration with the Dermatology Branch, NCI, demonstrated that cultures of XP conjunctival cells are deficient in the unscheduled synthesis of deoxyribonucleic acid for repair of UV damage, when compared with the conjunctival cells of an unaffected subject.